(O-14) Testosterone dose reduction in trans men does not affect serum hormone concentration nor increase the risk of erythrocytosis in trans men

Abstract Introduction Trans men may experience an increase of up to 6.9% in hematocrit (Hct) during gender-affirming hormone therapy with testosterone (GAHT-T), which can lead to increased blood viscosity and trigger cardiovascular events. Objective To evaluate the effect of administering 100 mg of testosterone cypionate biweekly on hematocrit levels and serum testosterone concentration over a three-month follow-up period. Methods This quasi-experimental study, part of a controlled trial, included trans men aged 18–40 years with a diagnosis of erythrocytosis secondary to testosterone use. Exclusion criteria were polycythemia vera or secondary polycythemia due to other conditions, hematocrit >55%, contraceptive use, or severe psychiatric disorders. All participants received 100 mg of testosterone cypionate biweekly for three months. A linear mixed-effects regression model was used to assess the influence of time on dependent variables. This project is registered at ClinicalTrials.gov (NCT05487794) and the Brazilian Clinical Trials Registry (ReBEC; RBR-479v8tv). Results Between September 2022 and November 2023, 21 trans men were evaluated (mean age: 26.6 ± 4.4 years; mean BMI: 26.9 ± 6.3 kg/m2). No increase in hematocrit levels was observed (baseline: 51.5 ± 1.2 g/dl vs. 3 months: 50.8 ± 1.7 g/dl; p = 0.076), nor in serum testosterone concentration (baseline: 362.1 [IQR: 300–637] ng/dl vs. 3 months: 494.4 [IQR: 310–709] ng/dl; p = 0.234). Conclusion Reducing the testosterone cypionate dose to 100 mg biweekly for three months in transgender participants with erythrocytosis did not increase hematocrit levels and maintained testosterone concentrations within the therapeutic target recommended for the development of male secondary sex characteristics. Financing EMS, Capes.